50 R. T. Günther 



I ueed hardh" add that tlie difficulty of distiuguishiiig a foreign 

 cell of leucocyte appearauce iu the midst of moUuscan conuective 

 tissue is ven great. 



The further history of the "young embryos"' is unknown. It 

 is possible that they niay develope into planulae whieh make their 

 way out of the PlniUirho'f' cither betöre or after its death, lead a free 

 swimming existence for a time and finally settle upon other PhijUirhoe 

 and grow iuto the mature Mnestra. Or, they may in tlie free state 

 grow into medusae whieh settle upon the PhyUirho'è. In auy case 

 we are met with the difficulty of imagining how a small organism 

 endowed with comparatively feeble swimming powers can succeed 

 in attaching itself to a particular region of the surface of a much 

 stronger swimmer. The '"throat" of the Phyìlirhoe is iuvariably mar- 

 ked by the special development of glandulär cells, even in specimens 

 whieh appear not to have been infested by Miiestra: it is possible 

 that a secretion exuded from this region may attract the Mnesti-a. 

 And certainly, if the Mitesira attached itself to most other parts of 

 the PJn/Uirhoe, the swimming powers of the latter would be greatly 

 impaired. 



One Observation would seem to indicate that in that particular 

 case the Mnestra had only recently become attached to the PhijUi- 

 rhoe and had led a free swimming medusa life until the said 

 attachment. In April a Mnestra, firmly adhering to a PhyUirhoe, 

 was captured, whieh had the shells of three pelagic organisms be- 

 longing to the family of the Tintinnoida in diverticula of its gas- 

 trie cavity (fig. 39). The Shells agreed well with the illustrations 

 of a variety of Bictyocysta poiymorpha (Géza Extz. in: Mitth. Z. 

 Stat. Neapel 6. Bd. pl. 1 4 figs. 3 and 4). Similar Shells are described 

 as having oceurred frequently in the stomach of Salpa and so it is 

 not surprising to find them in those of other pelagic animals. 



The purpose of the complete armare ent possessed by Mnestra 

 is not at first sight very clear. We cannot suppose that by its 

 nettle batteries it is euabled to numb victims and secure food for 

 itself, since with its mouth firmly anchored to the PhyUirhoe it 

 can neither procure nor devour prey. Mnestra is entirely dependent 

 upon its host for nutriment and ujion bis movements for opportunities 

 tor the discharge of the nematocvsts. 



